1. Field of Invention
This invention relates to techniques for monitoring the performance of a pump; and more particularly, this invention relates to techniques for monitoring the performance of a pump based at least partly on unsteady pressures or acoustic emissions sensed in relation to the pump using, e.g., SONAR-based and/or PVDF-based sensor technology.
2. Description of Related Art
Techniques are known for monitoring the performance of pumps, including the monitoring of various components of the pump, as well as monitoring the efficiency of the pump. The pumps may include among others centrifugal, bladder, piston or positive displacement pumps. The following is a brief description of some known pump conditions or parameters that are important to pump performance, known techniques for monitoring pump performance as well as some of drawbacks related to the known techniques:
For example, the slip of a centrifugal pump is an important parameter in determining the efficiency of the pump. The greater the slip the lower the effective efficiency. Wear in an impeller and/or a casing or liner of a pump can increase the slip and thereby reduce efficiency of the pump.
In addition, centrifugal pumps are used extensively throughout industry, in applications ranging from processing clean liquids through heavy slurries. A typical problem that these pumps can exhibit is cavitation near the impeller of the pump. The cavitation of small bubbles on the surface of the vanes of an impeller will erode and pit the impeller. This will result in degraded performance of the pump and if the conditions causing the cavitation are not rectified will likely cause impeller failure.
Moreover, it is known in the art that many aspects of the health of a pump can be obtained by taking accelerometer measurements in various locations on, or in relation to, a pump. Details of internal bearing health can be determined by the vibration readings obtained from the accelerometers and any excessive vibration can indicate damage to internal components. However, often these measurements provide information only after damage has occurred. Typically, wear components of a pump will likely induce vibrations in the pump and will also likely produce acoustic emissions. Existing systems are available that will monitor the airborne acoustics around a pump; however, these systems have to filter out the emissions from only the pump of interest. In addition, by the time the acoustic emissions become airborne they often have been attenuated greatly and are difficult to measure.
Further, leaks around bearings and mating surfaces can be a problem in high pressure applications if not quickly identified and fixed. Typically, a small high pressure leak will have an associated high frequency acoustic emission. This acoustic frequency will be higher than the vibration and other acoustic frequencies present on a typical pump.
Furthermore, one type of pump typically used for high viscosity or pressure applications are positive displacements pumps. These pumps operate by forcing fluid from an inlet pressure section of the pump into the discharge section. Several variations of these pumps exist, although most employ a valve or sealing mechanism to isolate the inlet from the discharge during the pressurization phase of the pump.
Finally, the overall efficiency of an electric-motor driven pump may be defined as the power delivered to the fluid (the water horsepower) divided by the electric power delivered to the motor:
      η    =                  Q        ×                  (                                    P              DISCHARFGE                        -                          P              INTAJKE                                )                    W        ,where:
Q=flow rate, m3/sec,
PDISCHARGE=Pump discharge pressure, Pa,
PINTAKE=Pump intake pressure, Pa, and
W=Electrical power, Watts.
The pump/motor efficiency will be less than one due to system losses which can include fluid leakage (through impeller clearances), friction, mechanical (bearings, seals, etc.) in the pump and the electric motor efficiency.
The operator of a pump will generally want to run the pump at the highest possible efficiency for a given set of flow conditions. However, over time as the pump is used the efficiency will decrease either 1) gradually due to normal wear or 2) suddenly due to mechanical failure or damage. In either case, there will be an optimum point at which maintenance action to restore lost efficiency would be beneficial. The operator's dilemma is deciding when to perform maintenance, because maintenance done too soon or too late can significantly impact overall cost to the operator.
The pump efficiency as defined above can be calculated by measuring the flow rate through the pump, the intake and discharge pressures (or the DP between the intake and the discharge) and the power to the electric motor.
In view of the aforementioned, there is a need in the industry for new techniques for the monitoring of the performance of pumps, including among others centrifugal, bladder, piston or positive displacement pumps.